Mailing systems, such as, for example, a mailing machine, often include different modules that automate the processes of producing mail pieces. The typical mailing machine includes a variety of different modules or sub-systems each of which performs a different task on the mail piece. The mail piece is conveyed downstream utilizing a transport mechanism, such as rollers or a belt, to each of the modules. Such modules could include, for example, a singulating module, i.e., separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering/printing module, i.e., applying evidence of postage to the mail piece. The exact configuration of the mailing machine is, of course, particular to the needs of the user.
Modern mailing machines utilize digital printing techniques for producing images on a mail piece being processed therethrough. Conventional digital printing techniques include bubble jet and ink jet, each of which produces an image in a dot matrix pattern. With digital printing, individual print head elements (such as resistors or piezoelectric elements) are selectively electronically stimulated to expel drops of ink from a reservoir onto a substrate, e.g., a mail piece. In either case, by controlling the timing of energizing of the individual print head elements in conjunction with the relative movement between the print head and the mail piece, a dot matrix pattern is produced in the visual form of the desired indicia, i.e., the evidence of postage.
Digital printing technology has significant advantages when used in a mail handling apparatus as compared to older technology that utilized either a flat platen or a rotary drum to imprint indicia on mail pieces. For example, if the variable indicia image data needs to be changed, it can easily be done through the installation of new or upgraded software versus having to replace the entire meter, since the flat platen and drum are typically not separately removable. Moreover, greater printing speeds can be obtained as compared to conventional mechanical printing systems. However, the use of a digital print head in a mail handling apparatus presents other issues that must be taken into consideration. For example, for the ink jet nozzles of an ink jet printer to properly deposit ink on the surface of the receiving medium, it is critical that a small predetermined gap be maintained between the exit plane of the nozzles and the surface of the receiving medium, typically in the order of one sixteenth to one thirty-second of an inch. This gap is necessary to achieve acceptable image quality, since too small a gap causes scuffing of the print head and to large a gap results in inaccurate dot placement, with either situation resulting in a deteriorated print image. Thus, in the mailing machine environment, it becomes necessary to maintain this critical gap between the exit plane of the ink jet nozzles and the upper surface of the mail pieces being conveyed through the mailing machine.
To accomplish this, the mail pieces, such as, for example, envelopes, postcards, flats, and the like, must be conveyed with the front panels on which the postage indicia is printed lying in a fixed registration plane, which is disposed beneath the exit plane of the nozzles a distance equal to the aforementioned gap. This arrangement is referred to hereinafter as top registration. The problem that arises, however, with top registration is that the plane of the rear panel of the mail piece is not fixed, as is the case with bottom registration, but rather must shift vertically in accordance with variations in the thickness of the mail pieces being conveyed through the mailing machine. Thus, even with top registration, the mailing machine must be capable of accepting mail pieces of varying thickness.
FIGS. 1 and 2 illustrate a portion of a conventional mailing machine, including a transport mechanism 10, that provides top registration of a mail piece. Transport 10 includes a support bracket 12 coupled to a support spring 14. One or more drive/idler rollers 16 are mounted to the support bracket 12. A belt 18 is looped around the drive/idler rollers 16. At least one drive roller 16 is coupled to a motor (not shown) that controls rotation of the drive roller 16, and hence movement of the belt 18. A registration plate 20 is situated above the belt 18. A print head 22 is mounted adjacent to the registration plate 20, situated over an opening (not shown) in the registration plate 20. Spring 14 maintains a biasing force on support bracket 12, and hence the belt 18, in the direction of the registration plate 20. As a mail piece 30 is transported by the movement of the belt 18 in the gap between the belt 18 and the bottom surface of the registration plate 20, the mail piece 30 is kept registered against the bottom surface of registration plate 20 by the force exerted from spring 14, thereby fixing the distance between the print head 22 and the top surface of the mail piece 30.
Excessive drag between the belt 18 and the bottom surface of the registration plate 20 is prevented by limiting the amount of movement of the support bracket 12 in the upward direction by a pair of adjustable up-stops 24. The adjustment of the up-stops 24 is critical, as the gap between the belt 18 and the registration plate 20 must be small enough to run card stock yet large enough to prevent the belt 18 from contacting the registration plate 20 when no card stock is present.
Most mailing machines are typically designed to handle mail pieces of different thickness, such as, for example, from card stock up to three-quarters of an inch thick. As such, the transport 10 must be displaceable to accommodate the thicker mail pieces. As a thicker mail piece is transported by the transport 10, the spring 14 will compress (as illustrated in FIG. 2), thereby allowing the mail piece to pass between the belt 18 and the registration plate 20, while still maintaining the registration of the mail piece against the bottom surface of the registration plate 20. Compression of the spring 14 will cause a small gap 40 between the support bracket 12 and the up-stops 24.
There are problems, however, with the conventional top registration transports such as transport 10. First, the transport 10, including the support bracket 12 and drive/idler rollers 16, is relatively large and heavy. Thus, the spring 14 must be strong enough to lift both the transport 10, along with a heavy mail piece, to ensure proper registration of the mail piece along the bottom surface of the registration plate 20. This makes it extremely difficult to provide fine adjustments to the gap. If the belt 18 make contact with the registration plate 20, the amount of friction between the two, caused by the force of spring 14, could damage the motor driving the belt 18 or even prevent the belt 18 from moving at all. It is thus necessary to always maintain the small gap between the belt 18 and registration plate 20 to prevent such damage to the motor or immobilization of the belt 18.
Second, when a thick mail piece exits the transport 10, the spring 14 will decompress until the support bracket 12 contacts the up-stops 24. Generally, this decompression and resulting movement of the support bracket 12 is both quick and forceful, causing a severe shock on the up-stops 24 and transport 10 when the support bracket 12 makes contact. The amount of displacement of the transport 10, and corresponding shock to the up-stops 24 and transport 10 upon return to its original position, increases as the mail piece thickness increases. The sudden decompression of spring 14 causes several problems. First, the noise associated with the support bracket 12 making contact with the up-stops 24 is substantial. Due to the fine adjustment required to maintain the small gap between the belt 18 and registration plate 20, it is not possible to provide any type of damping material to reduce the amount of noise, as any dampening material may deform over time, thereby decreasing the gap and allowing the belt 18 to make contact with the registration plate 20. As noted above, this is not an acceptable situation. In addition, the repeated force with which the transport bracket 12 contacts the up-stops 24 will, over time, affect the gap between the belt 18 and registration plate 20. It is therefore necessary to frequently perform maintenance on the transport 10 to re-adjust the up-stops 24, thereby ensuring that the gap between the belt 18 and the registration plate 20 is small enough to run card stock yet large enough to prevent the belt 18 from contacting the registration plate 20 when no card stock is present. This necessary maintenance increases the cost of owning a mailing machine, as well as increases the down time, i.e., time which the machine cannot be used. If the maintenance is not performed regularly to properly maintain the gap, the transport 10 may become inoperable if the gap has decreased (due to the unacceptable amount of friction between the belt 18 and registration plate 20), or may not properly register thin mail pieces, such as card stock, if the gap has increased. Either of these situations will result in dissatisfaction with the mailing machine.
Thus, there exists a need for a top registration transport that can effectively handle mail pieces of different thickness while alleviating the problems of the conventional transports.